Crop yield,N use efficiency,and environmental impact of a 14 year fertilization experiment with winter wheat and summer maize,carried out in fluvor aqutic soil in North China,were analyzed.The results show that Treatment NPK (150 kg hm^-2 chemical N fertilizer per crop plus a set rate of P and K fertilizer) has always been the highest in yield of either winter wheat or maize with the smallest annual variation.The average yield of winter wheat (over 14 years) and maize (over 13 years) was 5 261 kg hm^-2 and 7 633 kg hm^-2,respectively.Treatment 1/2OM (i.e.half of N from chemical fertilizer and the other half from organic manure) was slightly lower than Treatment NPK in average yield of the crops,but in Treatment OM (only or ganic manure applied at the same rates of N,P,K as those in Treatment NPK),the yields of winter wheat and maize on average were 22% and 16% lower than those in Treatment NPK,respectively,and varied significantly from year to year.The treatment showed a rising trend with the time in yield (p<0.05).The averaged N use efficiency was 60% for winter wheat and 61% for maize in Treatment NPK,51% and 56% in Treatment 1/2OM,and 34% and 43% in Treatment OM,respectively.Total N in the surface soil (0～20 cm) was increasing in all the above treatments,which were in the order of OM>1/2OM>NPK.The amount of N recovered by the plants plus N residue in surface soil (0～20 cm) accounted for 69%,75% and 69%,respectively in NPK,1/2OM,and OM.There was no evidence of downwards movement of NO₃^- to subsoil and the N₂O emission factors were less than 0.24% in all the three treatments.In contrast,NO₃^- content increased with the depth of soil profile to 100 cm in Treatment NK,of which the crop yields were not significantly different from those in CK (without fertilization) and the N use efficiency was almost equal to zero,but its N₂O emission factor was lower than those in Treatment NPK.These results indicate that in the investigated soil with winter wheat and maize crop in rotation,crop yields could be maintained at a high level by application of chemical N fertilizer at a rate of 150 kg hm^-2 and P and K fertilizers at a reasonable rate per crop season.In this case negative environmental impact was negligible.